First, open a project, then click on the "Tasks" tab. You will see a few sub-categories such as "open", "completed", etc. Click on +"NEW TASK" to create a new task.
Once inside the project, navigate to the icon list to pre-select any icons you intend on using during the lifecycle. This is required if you plan on using OneSurvey offline.
You can type in the search bar or manually search the categories by clicking on the dropdowns.
Once you find the icon you are looking for, select it then click the 'add' button. This will send it the the selected icons tab, which indicates it is now available in the Field Tools.